The present invention relates to a magnetic recording and reproducing apparatus, and more particularly to an electric circuit suitable for use in a magnetic recording and reproducing apparatus which is so constructed as to be able to perform recording and reproducing operations at the same time, and which has a rotating cylinder having a relatively small diameter on which a reproducing pre-amplifier is mounted.
In a magnetic recording/reproducing apparatus using a rotating magnetic head, a rotary transformer is generally used for signal transmission between the rotating head and a signal processing circuit, and one signal transmission channel formed of a rotary transformer is required for one rotating magnetic head. In Japanese patent application publication No. JP-A-63-74101, it is described how magnetic heads and electric parts are arranged on a rotating cylinder to attain dynamic balance. According to the arrangement, however, the number of rotary transformers for forming signal transmission channels increases as the number of magnetic heads is larger. That is, each channel is low in transmission efficiency, and crosstalk between channels increases. Further, it is impossible to form a desired number of channels in a limited space. In order to solve such problems, an apparatus in which amplifiers and a changeover switch are mounted on a rotating cylinder to reduce the number of rotary transformers for forming signal transmission channels is described in a Japanese patent application publication No. JP-A-59-96509.
In a case where circuit parts such as a reproducing pre-amplifier are mounted on a rotating cylinder as mentioned above, it is very important how electric power and a control signal are supplied to the circuit parts on the rotating cylinder, and it is also important to reduce elements for transmitting signals between the rotating cylinder and a fixed part. Further, in a case where recording and reproducing magnetic heads and a reproducing pre-amplifier are mounted on a rotating cylinder having a relatively small diameter such as the rotating cylinder of a home video tape recorder to perform recording and reproducing operations at the same time, however, the most important problem is to reduce jitter and crosstalk. In more detail, in a home video tape recorder which is required to be small in size and weight, the moment of inertia of a rotating cylinder is small. Accordingly, when electric parts such as a reproducing pre-amplifier are mounted on the rotating cylinder, it is very difficult for the rotating cylinder to attain dynamic balance. Thus, the so-called jitter is increased. Further, since the rotating cylinder has a relatively small diameter, a recording head and a reproducing head are arranged in close proximity to each other. Thus, the capacitance between the recording head and the reproducing head is increased, and moreover the capacitance between the wiring pattern for the recording head and the wiring pattern for the reproducing head is increased. Owing to the increase in capacitance between the recording and reproducing heads and the increase in capacitance between the wiring patterns, the crosstalk between a recording signal and a reproduced signal is increased. As a result, a beat or the like is generated. Thus, the picture quality of a reconstructed image is degraded. Further, in an apparatus for performing special reproducing operations such as a search operation and the formation of a still image, a relatively large number of magnetic heads and reproducing pre-amplifiers are mounted on a rotating cylinder. Accordingly, it is very difficult for the rotating cylinder to attain dynamic balance, and moreover elements for transmitting signals between the rotating cylinder and a fixed part are increased.